Journal of University of Chinese Academy of Sciences

Calculating the thermal stress of the moon in cooling process with 3-D viscoelastic model

JIN Yimin, TAO Sha, SHI Yaolin

2024, 41 (1): 1-10. DOI: 10.7523/j.ucas.2022.059

Thermal stress of the moon due to cooling process is non-negligible in lunar evolution. We calculate the accumulation of thermal stress with 3-D viscoelastic model, and explore the influence of viscosity parameters on thermal stress through comparative experiments. Numerical results suggest that the thermal stress of lithosphere is utterly distinct from deep mantle. The lithosphere is under tangential compression that concentrates at the bottom of the crust because of unevenly distributed cooling rate and elastic strength; on the other hand, the accumulation and relaxation of thermal stress in deep mantle is balanced due to low viscosity, and the thermal stress is in a “hydrostatic” state, which is mainly controlled by the elastic surface. Under the assumption that viscosity of lunar lithosphere is greater than 10²⁸ Pa·s, the tangential compressive stress in lithosphere accumulates to several hundreds of MPa in the present day, while the tensile stress in deep mantle reaches up to 100 MPa. Consequently, part of the shallow moonquake events can be explained by thermal stress. However, the focal mechanism of deep moonquakes is still unclear. We speculate that the tensile thermal stress in deep mantle helps to develop pore structures, and the melting layer provides pore fluid with high pressure, which reduces the fracture strength of mantle medium.

Learning path planning methods

LUO Zhongkai, ZHANG Libo

2024, 41 (1): 11-27. DOI: 10.7523/j.ucas.2022.061

Abstract ( 1168 ) PDF (0KB) ( 5 )

This review aims to guide the future development of related research in the field of learning path planning through the analysis of the current research status of learning path planning. Specifically, this review first introduces the definition of learning path planning and the commonly used parameters in learning path planning methods; then, it classifies in detail according to the algorithms used to generate learning path planning and summarizes the advantages and disadvantages of various learning path planning methods. In addition, the data set and evaluation method used by the learning path planning method is introduced. Finally, the challenges faced by the learning path planning method are summarized and the future development trend is predicted.

Continuity of the L^p-norm of the truncated Hardy-Littlewood maximal operator

WU Jia, WEI Mingquan, YAN Dunyan

2024, 41 (1): 28-34. DOI: 10.7523/j.ucas.2021.0073

Abstract ( 417 ) PDF (0KB) ( 0 )

This paper focuses on the continuity of L^p(Rⁿ)→L^p(Rⁿ)-norm of the truncated Hardy-Littlewood maximal operator M^b_a with two truncation parameters a and b. We first, respectively, present the left semi-continuity and right semicontinuity of ‖M^b_a‖_{L^p(Rⁿ)→L^p(Rⁿ)} with respect to θ=b/a, and then the continuity of ‖M^b_a‖_{L^p(Rⁿ)→L^p(Rⁿ)} is extended to infinity.

Nucleon resonances in γp→π^-Δ⁺⁺ photoproduction

ZHU Yiming, YANG Fuzhong

2024, 41 (1): 35-41. DOI: 10.7523/j.ucas.2021.0042

Abstract ( 512 ) PDF (0KB) ( 0 )

The first measured high-precision data on the differential cross sections and polarization observable beam asymmetry Σ for the γp→π^-Δ⁺⁺ reaction from the LEPS collaboration are analyzed within a tree-level effective lagrangian approach. In addition to the t-channel π and ρ exchanges, the u-channel Δ exchange, the s-channel N exchange, and the interaction current that is required by the gauge invariance, the s-channel nucleon resonance exchanges are further taken into account to reproduce the data of LEPS. Numerical results show that, the data on Σ can not be well reproduced when no contributions from the s-channel resonance exchanges are introduced. Further analyses show that, by including the contribution from the resonance N(1860)5/2⁺, both the data on the differential cross sections and beam asymmetry Σ can be well reproduced.

Curing process of 1,3-di(2'-aminoethyl)-2-methylimidazolium bromide with epoxy resin E-51

SU Ze, BAI Jinhu, WU Qiong, LIU Long, ZHANG Yanqiang

2024, 41 (1): 42-49. DOI: 10.7523/j.ucas.2022.049

Abstract ( 310 ) PDF (0KB) ( 0 )

A diaminoimidazole ionic liquid curing agent, 1,3-di(2'-aminoethyl)-2-methylimidazolium bromide (DAIL) is prepared via quaternization of imidazole rings. With epoxy resin E-51 as matrix resin, the curing process conditions of DAIL as curing agent and the properties of cured products are studied in depth. The results show that DAIL can be used as a medium temperature curing agent for epoxy resins. The optimal ratio of the two is DAIL∶E-51=20∶100, the optimal curing temperature range is 74~105 ℃, and the post-curing temperature is 162 ℃. The tensile strength of the cured cast body splines is 159 MPa, the elastic modulus is 2 281 MPa, and the elongation at break is 12.8%, the thermal decomposition temperature is 424.4 ℃. DMA analysis shows that the maximum loss factor tanδ of the DAIL/E-51 cast body is 0.56, and the glass transition temperature θ_g is 83 ℃, the corresponding storage modulus E is 290 MPa, and the crosslinking density is 30 149 mol·m^-3. This study provides an important experimental basis for the use of high mechanical properties of medium temperature epoxy resin curing agent.

Cause of thermal event moonquakes by thermos-elastic stress finite element models

ZHANG Junce, HU Caibo, SHI Yaolin

2024, 41 (1): 50-64. DOI: 10.7523/j.ucas.2022.045

Abstract ( 507 ) PDF (0KB) ( 0 )

On the basis of the previous work, considering the solar heat absorbed by the lunar surface inward and the lunar thermal radiation heat released outward, as well as the nonlinearities of the thermodynamic parameters of the lunar soil related to the temperature and depth, we have developed a thermo-elastic coupled finite element parallel program suitable for the study of the temporal and spatial evolutions of the temperature, deformation, and thermal stress of the lunar soil, and have utilized the four sets of finite element models to investigate the effects of the characteristic thicknesses of the lunar soil on the temporal and spatial evolutions of the temperature, deformation and thermal stresses of the lunar surface. The computational results show that the temperature of the lunar surface varies periodically over one lunar day (29.5 Earth days), and the temperature of the equatorial lunar surface varies from 100 to 385 K, with the variation decaying exponentially with the increase of the depth, and the depth of influence reaches to about 50 cm. The temperature cyclic changes also cause the vertical displacement of the lunar surface to rise and fall, and the horizontal normal stress of the lunar surface in the form of compression and tension. In general, the horizontal stresses are compressed during the day and tensile during the night, with the fastest increase in tensile stress at 18:00 and the highest tensile stress at 06:00. The characteristic thickness of the lunar soil has a strong influence on the temporal and spatial distributions of the temperature and the horizontal positive stresses. The magnitude of thermal stresses may reach the tensile strength of the lunar surface. The fastest growth of tensile stress and the period of maximum amplitude coincide with the observed high frequency of thermal events on the lunar surface in the morning and evening.

Application of infinite-spectral hybrid method in 2.5-dimensional gravitational potential calculation

REN Junsheng, ZHANG Huai

2024, 41 (1): 65-69. DOI: 10.7523/j.ucas.2022.041

Abstract ( 265 ) PDF (0KB) ( 0 )

Gravitational potential is an inseparable part of the earth’s free oscillation simulation. It is also the object of calculation in the study of gravity anomalies. Since the gravitational potential satisfies the unbounded Poisson-Laplace equation, which is zero at infinity, this is frustrating for numerical simulations. The purpose of numerical simulation is usually achieved by limiting the solution domain and approximating its boundary conditions. We attempt to use the infinite-spectral hybrid method to fit the infinity boundary directly and no longer approximate the boundary conditions. Considering the computational efficiency of the 3D Earth model, this study uses a 2.5-dimensional governing equation. Finally, numerical experiments verify the factual accuracy of this method.

Coseismic deformation of Maduo M_S7.4 earthquake in Qinghai, on May 22, 2021: numerical simulation analysis and geodynamic enlightenment

MENG Sichen, MENG Qiu, CHEN Qizhi, HU Caibo

2024, 41 (1): 70-80. DOI: 10.7523/j.ucas.2022.046

Abstract ( 269 ) PDF (0KB) ( 0 )

The Maduo M_S7.4 earthquake in Qinghai on May 22, 2021 is the only strong earthquake that occurred in Bayan Har block in recent years. The coseismic deformation and stress adjustment of the Maduo earthquake have been highly concerned by many scholars. In this paper, a three-dimensional parallel elastic finite element program for coseismic deformation simulation of large earthquakes is developed using split node technique. The correctness and effectiveness of the program were verified by comparing with the analytical solutions of the elastic seismic dislocation models. We calculated the coseismic deformation of the Maduo M_S7.4 earthquake and the coseismic Coulomb stress changes on the major faults in the research area. The results show that the surface coseismic deformation is consistent with those by different geodetic observation data and inversion results of some finite fault models. It also shows the earthquake is mainly a sinistral strike-slip fault with some normal fault components. Most aftershocks (magnitude>1.0 and depth of 9-11 km) except those besides the mainshock fault located in the regions of positive Coulomb stress changes at the depth of 10 km. The distribution of the Coulomb stress changes on the different fault zones is not uniform. The Coulomb stress changes on the southern end of Elashan Fault zone, the eastern end of Kunzhong Fault zone, most segments except some central-western parts of East Kunlun Fault zone, the northwestern segment of Dari Fault zone and the northwest and southeast segments and regions near the mainshock of Maduo-Gande Fault zone increase obviously, which requires more attention.

Calculation method of geometric parameters for decision support of “Zhurong” Mars rover leaving the landing platform

LI Hao, MA Youqing, ZHANG Shuo, LIU Shaochuang

2024, 41 (1): 81-87. DOI: 10.7523/j.ucas.2022.048

Abstract ( 362 ) PDF (0KB) ( 0 )

The departure of Zhurong Mars rover from the landing platform is the first key action performed after the Tianwen-1 detector system landing on Mars, and it is the basis for subsequent inspections of the Martian surface. In order to provide decision support for the safe departure of the rover, a method for calculating the angle between planes based on the three-dimensional image of the navigation camera is proposed to calculate the angle between the two departure orbit planes and the departure angle (the angle between the departure orbits and the surface of Mars). The process of decision support for Mars rover departure based on the navigation camera images is described. First, the forward intersection algorithm was used to obtain the coordinates of the point cloud on the surface of Mars and the coordinates of the departure orbits feature points. Then a plane fitting method combining the random sample consensus (RANSAC) algorithm and the total least squares method was used to fit the departure orbit plane and the surface of Mars, and the rationality and robustness of the method was verified through simulation experiments. At the end, the angle between the departure orbit planes (0.203°) and two departure angle (-18.947°, -19.154°) were calculated and used in the decision of Zhurong rover departure. On May 22, 2021, the Zhurong Mars rover successfully departed from the landing platform and set foot on the surface of Mars.

An improved UAV-borne DInSAR baseline estimation method based on interferometric phase period

ZHANG Tong, QIAO Ming, DANG Xiangwei, ZHONG Shengyiliu

2024, 41 (1): 88-96. DOI: 10.7523/j.ucas.2022.053

Abstract ( 324 ) PDF (0KB) ( 0 )

UAV (unmanned aerial vehicle)-borne differential interferometric synthetic aperture radar (SAR) has unique advantage and has attracted the attention of key research institutions at home and abroad in recent years. Baseline is a crucial parameter in differential in DInSAR processing, which is directly related to the accuracy of interferometric measurements. Compared with space-borne InSAR, UAV platform is difficult to keep the flight at the same track, and the flight attitude are unstable, which brings great difficulties to the baseline estimation of UAV-borne DInSAR. In this paper, starts from the characteristics of UAV platform and application scenarios, an improved baseline estimation method is proposed. This method derives the relationship between the interference phase period, the slant range, the distance between two ground points, and the phase difference through the interference geometric relationship. The distance between the two points is then substituted into the known parameters for baseline estimation using the least squares method. Comparing the simulation results and the actual data results of the original method and the improved method, it shows that the accuracy and robustness of the baseline estimation results of the improved method are significantly improved.

A remote sensing image registration method combining feature information clustering and partitioning

SHI Zhengyi, LIU Shuo, XIA Hao

2024, 41 (1): 97-106. DOI: 10.7523/j.ucas.2022.021

Abstract ( 237 ) PDF (0KB) ( 0 )

Aiming at the problem that the global registration model can’t correctly fit the local region due to topographic relief and rich ground object types, this paper proposes a method to quickly divide the image region and realize fine fitting based on feature information hierarchical clustering method. This method uses the scale constraint of difference space to extract the feature points of sift with higher accuracy, and optimizes the matching efficiency combined with Hellinger transform to complete the rough feature matching. The initial clustering is completed according to the point neighborhood information, and different models are obtained; the coincidence degree of matching points to different transformation models is calculated, the tendency set is constructed, the set is merged according to the distance to obtain the cluster center; and the sub region is generated using Tyson polygon method. The transformation model of each sub region is solved and interpolated to obtain the registration results. The remote sensing images of farmland, mountainous areas and coastal cities and towns are used for experiments. The registration effects of SIFT+ST, FSC-SIFT and PSO-SIFT methods are compared with this method. The results show that the accuracy and visual registration effect of this method are better.

An image matching algorithm combining local and semi-global geometry preservation

ZHENG Meiyan, CHEN Jun, GE Xiaoqing, ZHANG Hong

2024, 41 (1): 107-116. DOI: 10.7523/j.ucas.2022.019

Abstract ( 459 ) PDF (0KB) ( 0 )

Remote sensing image matching is an essential preprocessing step for many remote sensing applications. However, the distortions caused by elevation differences and the complexity of remote sensing image matching severely limit the matching precision of high-resolution remote sensing images. This paper proposes a robust feature matching algorithm suitable for local distortion and high outlier ratio. First, the Delaunay triangulation algorithm is used to impose geometric constraints on the initial matching point set, and the local adjacency relationship of the feature points is obtained. Second, pre-filter is conducted based on the adjacency information. Third, a multi-scale strategy is used to establish the local adjacency consistent model. Finally, a triangle similarity function is defined to achieve matching recovery. The experimental results on high-resolution images show that the average accuracy of our algorithm is 7.69% higher than that of RANSAC, and it is still robust when the outlier ratio is higher than 90%.

Local observation reconstruction for Ad-Hoc cooperation

CHEN Hao, YANG Likun, YIN Qiyue, HUANG Kaiqi

2024, 41 (1): 117-126. DOI: 10.7523/j.ucas.2022.028

Abstract ( 530 ) PDF (0KB) ( 0 )

In recent years, multi-agent reinforcement learning has received a lot of attention from researchers. In the study of multi-agent reinforcement learning, the question of how to perform ad-hoc cooperation, i.e., how to adapt to a changing variety and number of teammates, is a key problem. Existing methods either have strong prior knowledge assumptions or use hard-coded protocols for cooperation, which lack generality and can not be generalized to more general ad-hoc cooperation scenarios. To address this problem, this paper proposes a local observation reconstruction algorithm for ad-hoc cooperation, which uses attention mechanisms and sampling networks to reconstruct local observations, enabling the algorithm to recognize and make full use of high-dimensional state representations in different situations and achieve zero-shot generalization in ad-hoc cooperation scenarios. In this paper, the performance of the algorithm is compared and analyzed with representative algorithms on the StarCraft micromanagement environment and ad-hoc cooperation scenarios to verify the effectiveness of the algorithm.

Design and implementation of fuzzy extractor for PUF

SONG Minte, HOU Kai, RU Zhanqiang, WANG Zhengguang, SONG Helun

2024, 41 (1): 127-135. DOI: 10.7523/j.ucas.2022.054

Abstract ( 518 ) PDF (0KB) ( 5 )

The physical unclonable function (PUF) implemented on SRAM and other schemes exists inherent demerit of poor reproducibility for environmental factors such as voltage changes and thermal noise. This disadvantage greatly restricts functional application in cryptography, communication and other fields. In this paper, a fuzzy extractor with large error correction capacity is designed to reconstruct the original data of SRAM by means of BCH codes (Bose-Chaudhuri-Hocquenghem Codes). The SRAM PUF chip applying this design is manufactured on the Hua Hong Grace 0.11 μm CMOS platform with area of 306 267 μm². The original BCH code has a code length of 127 bits and an error correction capability of 27 bits, which achieves the practical requirements of PUF applications.

Identification of core rumor spreaders in online social networks based on multi-stage deep model

LI Yuan, ZHANG Qi, ZHU Jianming, JIAO Jianbin

2024, 41 (1): 136-144. DOI: 10.7523/j.ucas.2022.057

Abstract ( 586 ) PDF (0KB) ( 6 )

Online social networks have become the disaster areas where rumors grow. It is of great significance to identify core rumor spreaders for rumor prevention and control. The traditional rumor control model is mainly based on the dynamics of rumor propagation, and it is mainly focused on in-event or post-event control. In view of the timeliness of rumor control, this paper proposes a multi-stage graph convolutional network based on multi-dimensional features (MSF-GCN) deep learning model to accurately locate core rumor spreaders as early as possible and block rumor diffusion from the source. This work compares the MSF-GCN method with other three baseline methods on rumor data set, and the experimental results verify that our method is more efficient.

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